In the very beginning of the Civil War, prisoners of war were exchanged right on the battlefield, a private for a private, a sergeant for a sergeant and a captain for a captain. In 1862 this system broke down and caused the creation of large holding pens for prisoners in both the North and South. On July 18, 1862, Major General John A. Dix of the Union Army met with the Confederate representative, Major General Daniel H. Hill, and a cartel was drafted providing for the parole and exchange of prisoners. This draft was submitted to and approved by their superiors. Four days later, the cartel was formally signed and ratified, and became known as the Dix-Hill Cartel.

The Dix-Hill Cartel failed by midyear, for reasons including the refusal of the Confederate Government to exchange or parole black prisoners. They threatened to treat black prisoners as slaves and to execute their white officers. There was also the problem of prisoners returning too soon to the battlefield. When Vicksburg surrendered on July 4, most of those Confederate prisoners who were paroled were back in the trenches within weeks.

The discussions on exchange lasted until October 23, 1862, when Secretary of War Edwin M. Stanton directed that all commanders of places of confinement be notified that there would be no more exchanges. This decision would greatly affect the large numbers of prisoners in northern and southern prison camps. The so-called "holding pens" now became permanent prisons.

Although more than 150 places were used as prisons on both sides during the war, only a handful are important. Generally they fit into certain types: the fortifications, former jails and penitentiaries, altered buildings, enclosures around barracks, enclosures around tents and open stockades.

Of the first type, the only important example in the Confederacy is Castle Pinckney. The Union had Fort Warren in Boston Harbor, Fort Lafayette in N.Y., Fort McHenry in Baltimore and, most dreaded in the South, Fort Delaware in the Delaware River. The Union used the Alton, Ill., and the Columbus, Ohio, penitentiaries for prisoners, and the Confederate cavalryman, John Morgan, escaped from the latter.

The Confederacy's Libby Prison and the Union's Old Capitol and Gratiot Street Prisons were converted buildings. Others, all in the South, where tobacco factories were common and excellent for this purpose, were Ligon's in Richmond and Castle Thunder in Richmond and Petersburg. Buildings were also converted in Danville, Lynchburg, and Shreveport, and Cahada (Ala.) was one of the more important ones.

Union prisons that were enclosures around barracks included Johnson's Island, Camp Morton, Camp Douglas, Camp Chase, Elmira, and Rock Island. The Confederate Belle Isle and the Union Point Lookout prisons were enclosures built around tents. Prisons that were open stockades existed only in the South, and the most infamous was Andersonville. Others of this type were Camp Lawton, Camp, Camp Ford Camp Groce, and stockades at Salisbury (N.C.), Macon (Ga.), Charleston, Florence (S.C.), and Columbia (S.C.).

"The Civil War Dictionary" by Mark M. Boatner III and The Historical Times "Encyclopedia of the Civil War."